1. Field of the Invention
The present invention relates generally to centrifuge mechanisms, and more particularly to equipment for removing excess water from solids, such as de-watering leafy vegetable matter after washing and liquid-solid filtration.
2. Description of the Prior Art
Centrifugal food drying is currently being used to remove water from prepared salads after washing, to extract excess oil from chips and snacks, to salvage chocolate and nut meats from stale candy, to remove excess fat from meats and to extract juice and pulp from fruit. For example, Bock Engineered Products, Inc. (Toledo, Ohio) markets an "FP" series of centrifuges for dry weight capacities ranging from thirty-five pounds to 130 pounds. The Bock FP centrifuges includes a stainless steel basket, lid and cover. A fluid drive power transfer system spins the basket on a vertical axis and is stated to be self-balancing. The units are bolted to a floor with a tripod arrangement. A high volume model, FP-90, comes with a stainless steel lifting yoke, a basket floor dolly, a waterproof timer and a grid liner. A high-volume/multi-product model, FP-900, has a basket tachometer, stainless steel base and legs, stainless steel back panel, hydrostatic variable speed control, stainless control circuit housing, stainless steel basket lifting yoke and a waterproof timer. The basket operates at a maximum of 1200 to 1700 revolutions per minute, depending on the manufacturer involved, to obtain a G-force of 600 to 980. The United States Department of Agriculture (USDA) has a program for approving such centrifuges in food processing. Operation of the Bock FP centrifuges includes a six step process.
In a first step, a hoist is used to put the basket into the centrifuge. The basket pins are checked to see that they are securely seated into the lifting yoke. A second step is to load the basket evenly. An improved drying is obtainable by placing a back-up grid in the basket before loading. The back-up grid can remain in place when dumping later. Leafy foods can be loaded to the top of the basket. Heavier foods, such as carrots and onions, are loaded no higher than the top of a centerpost in the basket. The maximum dry weight load is not recommended to exceed 130 pounds, and the basket can be loaded either inside or outside the machine. In a third step, the basket is guided into the machine by holding the inner rim of the basket, then unhooking and removing the yoke. In a fourth step, the inner rim of the basket is rotated by hand until firmly seated on a drive ball. The lid is closed and a start button is pressed to begin the automatic cycle. Bock cautions its users that the basket must be fully seated on the drive ball. In a fifth step, after a red indicator light goes out, the lid may be opened and the yoke is hooked to mating pins to lift the basket out. Bock cautions its users never to open the lid while the basket is moving, otherwise severe injury can result. In a sixth step, the contents of the basket are dumped by holding the inner rim and rotating the basket on the yoke.
A similar de-watering centrifuge is marketed by Gabilan Manufacturing, Inc. (Salinas, Calif.). The Gabilan unit is offered commercially for spin-drying lettuce, cabbage, spinach, onions, celery, carrots and other processed vegetables and other industrial applications. The Gabilan model GC10001p uses a three-point suspension system and a 8.9 cubic foot basket that rotates on a vertical axis within a stationary drum with a cover. Dry weight process capacity has been published by Gabilan as being 140 pounds for chopped lettuce, 175 pounds for shredded cabbage and forty pounds for whole leaf spinach. The basket operates at a maximum of 1076 revolutions per minute.
A fully automatic vegetable spin dryer is marketed by Sanborn (Wrentham, Mass.) as the SANBORN Model P. Drying applications include spinach, salad mix, cole slaw mix, shredded and chopped lettuce, shredded and chopped cabbage and related vegetables, e.g., onions, carrots, etc. The SANBORN Model P appoints itself to eliminating manual operations in the drying process by having a feed conveyer to load a spin dryer that rotates on a vertical axis, a product discharge cone that opens up the bottom of the spin dryer and a take-away conveyer system on which the product drops from the spin dryer. An inner basket is forty inches in diameter by twenty-four inches in height and is adjustably rotated up to 1100 revolutions per minute. A five step process is involved.
In a first step, a feed system controls the batch sizes and automatically loads the spin dryer, with the objective of consistent capacity from load to load. In a second step, the spin dryer operates at a low speed during the feed cycle to distribute wet product evenly around an inner basket. In a third step, the spin dryer automatically initiates the drying cycle at the end of the feed cycle. The rotational speed of the basket is increased to a drying speed and spun for a predetermined period. In a fourth step, a discharge cycle causes the spin dryer to decelerate to a "safe" unloading speed and the product discharge cone is released. The dried product falls out to the take-away conveyor. In a fifth step, the product discharge cone is raised back to its closed position and the spin dryer is re-accelerated to feeding speed, and the five-step cycle is repeated.
In general, conventional vertical centrifuges receive batches of produce to be de-watered in cylindrical perforated metal baskets. The baskets have a central female shaft hexagonal socket in the bottom which slip fits on the male hexagonal vertical drive shaft in the machine frame. The machine frame is very heavy to contain fragments should the basket breakup during the centrifuging process, as sometimes happens because of uneven loading.
The centrifuge shaft thus both supports and drives the basket, sometimes through a modified gimbals to adjust for uneven loading. The uneven loading, which run the basket out of balance, can trip a vibration safety switch, which will cut off power. The basket load of produce then must be manually redistributed before the centrifuge can accelerate to full speed for the de-watering process.
In some prior art machines there is a twin door opening bottom to discharge the de-watered produce, while in others the produce is removed by hand through the top opening of the basket. The machines are generally furnished with two or more baskets, since each one must be individually loaded, lifted, transported and set down into the centrifuge for the centrifugal operation, then lifted out and suspended over a receiving facility, where the bottom is opened for unloading. Baskets without bottom doors must be inverted to unload.
Because of their size and weight, the baskets are usually handled by overhead hoists mounted on monorails, and therefore, a typical de-watering system requires a relatively large area and several operators. Frequent repairs are necessary because of the damage sustained from uneven loading.
Since washing processes are usually continuous, elimination of the basket loading, unloading and moving requirement would both improve the process and reduce the cost. An open-ended cylinder that is spun rapidly on a horizontal axis can be used for de-watering. Uniform loading is simple and readily obtainable, and eliminates out of balance problems that can have catastrophic consequences.
A better method of de-watering washed or rinsed leafy vegetables such as lettuce or spinach is therefore needed in the vegetable drying industry.